More than 211,000 women will be diagnosed with invasive breast cancer this year and the National Cancer Institute estimates that there are currently 2.3 million breast cancer survivors in the United States. Cancer-related cognitive impairment is a significant concern for women diagnosed with breast cancer and 20-30% of women report cognitive difficulties, including problems with attention, concentration, and memory, at some point following diagnosis and treatment. Thus, more than one half million women may be facing adverse changes in cognitive function that can interfere with resumption of pre- cancer life roles and recovery of overall quality of life. Cancer-related cognitive change is poorly understood and we know little about the nature and course of the cognitive difficulties women with breast cancer experience in their everyday lives. Even less is known about the psychosocial and situational factors that may contribute to these cognitive changes. Short-term use of daily field diaries of cognitive failure events can provide insight into these experiences. We propose collecting 7-day daily diary reports of specific cognitive difficulties, life stressors, state affect, and fatigue at each of three assessment points;before treatment (baseline), during chemotherapy (T1), and 1 month after completion of chemotherapy (T2). The specific aims are 1) to describe the nature and frequency of cognitive difficulties that women with breast cancer experience and the real-life context in which these difficulties occur;2) Examine relationships among daily cognitive failure events and objective cognitive function, 3) Delineate the psychosocial profiles of patients who experience objective deficits in cognitive function. We will examine psychosocial, demographic, and clinical variables in an effort to identify factors associated with objectively measured, criterion defined, cancer-related cognitive changes. This proposal presents a novel approach to the study of the cognitive sequelae of breast cancer. Findings will be used to refine screening and assessment strategies for early identification of women vulnerable to cancer-related cognitive changes, and will guide the design of educational and rehabilitative interventions to target specific cognitive difficulties, improve overall cognitive performance, and improve quality of life. to Public Health Cancer-related cognitive difficulties, including problems with memory and attention, are a significant concern for breast cancer patients and survivors and can interfere with women's return to pre-cancer life roles and overall quality of life. However, researchers know very little about the everyday cognitive difficulties women experience in their lives or why some women have more severe cognitive problems than others. A better understanding of these issues will help health care providers identify women at risk for cancer-related cognitive difficulties and will guide the design of educational and rehabilitative interventions to target specific cognitive difficulties, improve overall cognitive performance, and improve quality of life.